[Exim] Multiline SMTP error messages

I have a requirement from $orkplace that needs to send users a pretty
long error message under certain conditions during the SMTP session.
Exim does this fine except it's breaking up the error message in to
three lines each prefixed with 550. This wouldn't be a problem except
most of our users are using Outlook Express which chokes on multiline
error messages. How can I get Exim to stick the entire error on a single
line instead of breaking it up? It worked automagically in Exim 4.10 but
this is 4.14 and I can't get it to quit inserting the line breaks.
Shortening the error message isn't an option unfortunately. :-(

TIA

Paul